Improvement of functional properties of β-lactoglobulin by conjugation with glucose-6-phosphate through the Maillard reaction

beta-Lactoglobulin (beta-Lg) was conjugated with glucose-6-phosphate (G6P) through the Maillard reaction by incubation at 50 degrees C and 65% relative humidity. It was considered that the preferable incubation time was less than 1 day because modification of amino group proceeded quickly through 1 day of incubation and then slowed down; the brown color development and polymerization of beta-Lg proceeded steadily from 1 day on. The beta-Lg treated with G6P for 0.5 days, of which phosphorus content was 1.06%, was estimated to conjugate 6.9 mol G6P per 1 mol beta-Lg. beta-Lg-G6P conjugate was completely soluble after heating its solution at 95 degrees C for 10 min whereas more than 90% of intact beta-Lg was precipitated at 90 degrees C. Emulsifying properties of beta-Lg were improved by conjugation of G6P. No calcium and phosphate were sedimented at 1000 g in the solution containing 30 mM calcium, 22 mM phosphate, and 10 mM citrate at pH 6.7 in the presence of 2% beta-Lg-G6P conjugate, but 14.5 mM calcium and 9.1 mM phosphate were sedimented at 100 000 g. The particules of the complex of the beta-Lg-G6P conjugate and calcium phosphate with 30-200 nm of diameter were observed in electron micrograph. It was concluded from the above results that modification of beta-Lg with G6P was useful in improving its functional properties. (C) 1998 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.